Alcohol/Drugs

Know your BAC

What is BAC?

Blood Alcohol Concentration

Blood Alcohol Concentration (BAC) is a measure of the percentage of alcohol in the bloodstream. A BAC of .20 means 2 drops of alcohol for 1,000 drops of blood. It is important to understand the factors that affect BAC and how the effects of drinking alcohol vary among individuals.

You can learn more about BAC in a virtual bar known as the Blood Alcohol Educator. This interactive software demonstrates how different drinking scenarios affect Blood Alcohol Concentration. By re-creating realistic drinking experiences, you will be able to see how the same amount of alcohol can affect others of different weight and gender.

Keep in mind that the impairment experienced at any blood alcohol level is dependent on one’s tolerance to alcohol. Tolerance is a measure of how sensitive a person is to alcohol’s effects. The higher our tolerance, the less able we are to tell when we are impaired. Therefore, those with a low tolerance to alcohol will notice effects at lower BACs, while those with a higher tolerance will notice them somewhat later.

Defining “A Drink”

The size of a container is not the best way to measure “a drink." To make low-risk drinking choices and avoid negative consequences as a result of drinking, we need a standard measure that will apply to different kinds of alcoholic beverages regardless of how they are served.

Beer – Most domestic beer is 4 to 5% alcohol, served in 12-ounce cans or bottles. This means an average beer contains about ½ ounce of pure alcohol.

Wine – The average table wine contains 12% alcohol, so 4 ounces of wine would contain about ½ ounce of pure alcohol.

Measured in this way – beer, wine, and liquor contain about ½ ounce of pure alcohol, which is a little more than the average amount of alcohol that the body can metabolize in one hour. ½ ounce of pure alcohol is the standard definition of "one drink." Using this definition, you can see how some “single serving" drinks may be the equivalent of two or more standard drinks, depending on the glass or container size.